Track circuit apparatus



Nov. 25,1941. P. N. MARTIN ETAL 2,264,091

TRACK CIRCUIT APPARATUS Filed Sept. 24, 1940 VVIVY H 7B 2 P 5 5 W 7 H1? 5 v 8 I l 9 4 Paul and B Pau/ 63 0 THEIR ATILORNEY Patented Nov. 25, 1941 UNITED STATE S PTE T FF I Q E TRACK CIRCUIT APPARATUS Paul N. Martin,

Penn Township,

Allegheny Vania Application September 24', 1940, Serial No. 358,124

6 Claims.

Our invention relates to track circuit apparatus and more particularly to apparatus of this character having high shunting sensitivity and positive shunt characteristics under the condition of varying resistance of the train shunt.

One object of our invention is to provide aprimary-secondary track relay combination having high shunting sensitivity.- Another object of our invention is to provide a combination in which the track relay is prevented from picking up due to an intermittent shunt and in which the likelihood of an undesirable pumping action under certain conditions between the primary and secondary relays is prevented.-

We accomplish the foregoing objects by causing the two full coils of the primary relay to be connected in parallel under the pick-up condition and causing, a stick contact on the primary relay to cut out a portion of one of these coils and to connect the remaining portion in parallel with the other coil over a compensating series resistor under the normal or holding condition.

We shall describe two forms of apparatus embodying our invention and shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1- is a diagrammatic view showing one form of track circuit apparatus embodying our invention, whereas Fig. 2 shows a modified form of the apparatus of Fig. 1, also embodying our invention.

Similar reference characters refer to similar parts in each of thetwo views.

Referring to Fig. 1, the rails of the track circuit section shown therein are supplied with current from a source TB located at one end of the section, over the usual current;- limiting resistor R. Connected across the rails at the other end of the section is the primary relay P which con trols the energization of the secondary relay S, these two relays together comprising the primary-secondary track relay combination. The secondary relay S may be of the slow pick-up type as shown in the drawing, although for certain applications, it may be preferable to use the usual ordinary-acting relay, without the time delay feature.

The primary relay P has the usual two coils or windings 2 and 3 but instead of being connected in series with one another as has been the usual practice, these coils are included in two parallel branches one of which is permanently connected across the rails and the other of which is closed over either a contact of the secondary relay S to provide a pick-up-circuit or over a contact of the primary relay itself to provide a holdingcircuit, thus obtaining certain op erating advantages which will be explainedhereinafteri Coil 2 of the primary relay P is connected directly across the track rails at all times, and at pick-up, the full winding of coil 3 is also connected across the rails, in parallel with coil ,2, over the back contact 4-5 of the secondary relay S. Under the holding condition, only a portion of coil 3 is connected across the rails, this connection being made over a compensating resistor CR which compensates for the resistance of that portion of coil 3' which is excluded from the holding circuit,v the connection also including the front contact 6 of relay P.

Under normal conditions when the track section is unoccupied, relay S is maintained energized over the front contact l of relay P', the current being supplied from any convenient source having the terminals B-'C, so that the lower portion of coil 3 is disconnected at the back contact 4-5 of relay S which is now open. The holding circuit for relay P is closed over the stick con tact 6, resistor CR, and upper portion of coil '3 so that relay P remains picked up and is maintained in a responsive state in preparation for sensitive release when the section becomes occupied.

When a train enters the section, the train shunt causes the current to decrease both in coil 2 and in the holding portion of coil 3 which is in multiple therewith, thus causing relay P to release. Contact I will open the energizing circuit for relay S, causing this relay to release arid to close back contact i'5 which connects the full winding of coil 3 in parallel with coil 2', in preparation for pick-up of relay P. The holding circuitwill be open at stick contact 6' and the apparatus will remain in this condition during the time that the section remains occupied; When the train leaves the section, pick-up current will flow in winding 2 and the full winding 3 so that relay P will pick up, restoring relay S to its picked-up position over front contact I and closing the holding circuit at front contacts 9 and 6 before the pick-up circuit isin'terrupted at back contact 5. When b ack contact 5 opens, the holding circuit alone will be efiective and the apparatus will be restored to the condition in which it isillustrate-d.

The use of a stick contact such as t in the ho1d ing circuit of a primary relay is advantageous. for the reason that once the primary relay releases sufficiently to open the stick contact, a full release is insured, even if the shunt is'temporarily lost thereafter because no adequate energiz'ingcir'cuit for the primary relay is available until the secondary relay goes through its release cycle. Since, however, it is desirable for purposes of sensitive shunting to decrease the holding energy for the primary relay as much as possible, the stick contact in the usual primary relay with series connected coils is a relatively weak contact having low contact pressure and frequently developing high resistance. The result of such high resistance in the holding circuit. is obviously to cause the primary relay to release even though the section is unoccupied, whereupon relay S releases, closing the pick-up circuit for relay P so that the cycle is periodically repeated. Thisre-- sults in an undesirable and continued pumping action of the relays P and S and intermittent flashing of any signal or other function which may be controlled over the contact 8 of relay S.

By connecting the coils 2 and 3 of relay P in the manner disclosed herein, the foregoing difficulty is completely overcome without in any manner reducing the sensitivity or safety of the track relay combination. It will be apparent that should the stick contact 6 develop high resistance, the effect of this resistance on the hOlding energization of the primary relay will be very much smaller than in the case of the series connected relay because one coil 2 is always in the rail circuit so that only the current in the holding portion of coil 3 will be aifected. Thus, a much greater operating margin is provided by the apparatus embodying our invention. The holding energy can, of course, be adjusted to the same value as in the series connected relay, so that the same shunting sensitivity can be obtained with our apparatus. This apparatus is not any more likely to result in undesired operation of the primary relay due to the effect of an intermittent shunt before relay S releases than the usual series coil arrangement, because the likelihood of relay P picking up on but one coil is so very remote that for all practical purposes it is equivalent to interrupting the energy completely and can accordingly be disregarded. The advantage in using a slow pick-up relay for relay S is that greater opportunity is provided for the flux in relay P to reach its steady value before relay S picks up and also that this saturation of relay P is less dependent upon the voltage effective across relay S. However, the purpose of the delay period is mainly to delay the closing of signal circuits in a given block before the secondary relay for the advance block has released. Where this is not a problem, an ordinary-acting secondary relay may be entirely satisfactory for the purposes of our invention.

The contact finger 4 should preferably be of the continuity transfer type, as indicated in Fig. 1, in order that the pick-up circuit for relay P will not be interrupted at back contact 5 until after the holding circuit is closed at front contact 9, during pick-up of relay S. If a continuity transfer contact is not desired, then the circuit of Fig. 1 can be modified by eliminating front contact 9 and wire l0, and connecting the points X and Y together. The latter arrangement will provide entirely satisfactory operation, the only difference being that the lower portion of winding 3 will now be shunted by resistor CR as soon as relay P picks up, thus decreasing slightly the energization of this relay during the pick-up time of relay S. In the Fig. 1 circuit the decrease of energization will not occur until front contact 9 closes, thereby providing an increased time during which the flux can build up in the primary relay before the energization is decreased.

Referring now to Fig. 2, we have shown therein an arrangement similar to Fig. 1 with the exception that for greater efficiency, the full winding of coil 3 is used in both the pick-up and holding circuits, the holding resistor HR. being introduced into the holding circuit by the stick contact 6 to cut down the energization to the desired level. Front contact 9 of relay S is eliminated in this figure so that the holding circuit includes contact 6 only. The operation of the apparatus of Fig. 2 is otherwise substantially the same as in Fig. 1 so that this operation will be clear without further detailed description.

From the foregoing, it will be apparent that we have provided a primary-secondary track relay combination which has all the advantages of the usual series connected primary relay but has, in addition, increased operating margins which render the apparatus less subject to improper operation when high resistance develops in the holding circuit of the primary relay.

Although we have herein shown and described only two forms of apparatus embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims Without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

1. In combination with a section of railway track and a source of track circuit current connected across the rails of said section, a primary relay energized from said source over the rails of said section, said primary relay having two energizing coils one of which is permanently connected across the rails of said section, a secondary relay energized over a front contact of said primary relay, means including a back contact of said secondary relay for connecting the other coil of said primary relay in parallel with said one coil across the two rails for providing pick-up energization for said primary relay, and means including a front contact of the primary relay and a resistor for connecting a portion of said other coil in parallel with said one coil to thereby provide holding energization for said primary relay.

2. In combination with a section of railway track and a source of track circuit current connected across the rails of said section, a primary relay energized from said source over the rails of said section, said primary relay having two energizing coils one of which is permanently connected across the rails of said section, a secondary relay energized over a front contact of said primary relay, means including a back contact of said secondary relay for connecting the other coil of said primary relay in parallel with said one coil across the two rails for providing pick-up energization for said primary relay, and a path in parallel with said one coil and including a, front contact of said primary relay for energizing said other coil at a reduced ampereturn value to thereby provide holding energization for said primary relay.

3. In combination with a section of railway track and a source of track circuit current connected across the rails of said section, a primary relay energized from said source over the rails of said section, said primary relay having two energizing coils one of which is permanently connected across the rails of said section, a secondary relay energized over a front contact of said primary relay, means including a back contact of said secondary relay for connecting the other coil of said primary relay in parallel with said one coil across the two rails for providing pickup energization for said primary relay, and means including a front contact of the primary relay and a resistor for connecting said other coil in parallel with said one coil to thereby provide holding energization for said primary relay.

4. A primary-secondary relay comprising, in combination, a primary relay having two energizing coils, one of which is arranged to be permanently connected across the energizing source, a secondary relay energized over a front contact of said primary relay, means including a back contact of said secondary relay for connecting the other coil of said primary relay in parallel with said one coil to provide pick-up energization of said primary relay, and means including a front contact of the primary relay and a resistor for connecting a portion of said other coil in parallel with said one coil to provide holding energization for said primary relay.

5. A primary-secondary relay comprising, in combination, a primary relay having two energizing coils, one of which is arranged to be permanently connected across the energizing source, a

secondary relay energized over a front contact of said primary relay, means including a back contact of said secondary relay for connecting the other coil of said primary relay in parallel with said one coil to provide pick-up energization of said primary relay, and a path in parallel with said one coil and including a front contact of said primary relay for energizing said other coil at a reduced ampere-turn value to thereby provide holding energization for said primary relay.

6. A primary-secondary relay comprising, in combination, a primary relay having two energizing coils, one ofwhich is arranged to be permanently connected across the energizing source, a secondary relay energized over a front contact of said primary relay, means including a back contact of said secondary relay for connecting the other coil of said primary relay in parallel with said one coil to provide pick-up energization of said primary relay; and means including a front contact of said primary relay, a front contact of said secondary relay and a resistor for connecting a portion of said other coil in parallel with said one coil to provide holding energization for said primary relay.

PAUL N. MARTIN. PAUL H. CRAGO. 

